Cultured fibroblasts have been shown to both phagocytose and degrade mast cell granules. This phagocytis process is both time and temperature dependent, and results in an increased rate of enzyme secretion from fibroblasts. This ability of fibroblasts to remove mast cell granules may represent an important mechanism by which immediate hypersensitivity reactions are terminated. In studies using human lymphocytes, mast cell granules were found to inhibit lectin-induced blastogenesis. This effect persisted after histamine removal. The inhibitory factor was shown to be heparin proteoglycan. Thus, mast cell granules, by virtue of their heparin content, can alter lymphocyte function. Human basophils were found to contain a chondroitin sulfate proteoglycan rather than heparin. This chondrontin sulfate could be released using calcium ionophore. Functional capabilities examined included anticoagulent activity and histamine-binding capacity.